In recent years, piezoelectric vibrators using crystals or the like have been used in mobile phones or personal digital assistants, as a time source or a timing source such as a control signal, or a reference signal source and the like. Various types of piezoelectric vibrators are known. As one of them, a Surface Mount Device (SMD) type piezoelectric vibrator is known.
FIG. 18 is a plane view of a state in which a lid substrate of a piezoelectric vibrator according to the related art is removed, and FIG. 19 is a cross-sectional view taken from line D-D of FIG. 18. As shown in FIG. 19, as an SMD type piezoelectric vibrator 200, a piezoelectric vibrator, in which a package 209 is formed by a base substrate 201 and a lid substrate 202, and a piezoelectric vibrating reed 203 that is received in a cavity C formed in an inner portion of the package 209, is suggested. The base substrate 201 and the lid substrate 202 are bonded to each other by anode-bonding by arranging a bonding film 207 therebetween.
It is generally desirable with piezoelectric vibrators that the equivalent resistance values (effective resistance value, Re) of the piezoelectric vibrator are suppressed to a lower level. Since piezoelectric vibrators with low equivalent resistance values can vibrate the piezoelectric vibrating reed using less electric power, they are more energy efficient piezoelectric vibrators.
As one of the common methods of suppressing the equivalent resistance value, there is known a method of making an inner portion of the cavity C with the piezoelectric vibrating reed 203, as shown in FIG. 18, sealed therein closer to a vacuum, thereby lowering a series resonance resistance value (R1) that is in a proportional relationship with the equivalent resistance value. As a method of making the inner portion of the cavity C closer to a vacuum, there is known a method (gettering) of sealing a getter material 220 formed of aluminum or the like in the cavity C and irradiating a laser from the outside to activate the getter material 220 (see Patent Documents 1 and 2). According to this method, since the oxygen generated at the time of anode-bonding can be absorbed by the getter material 220 entering the activation state, the inner portion of the cavity C can be made closer to a vacuum.
Patent Citation 1: JP-A-2006-86585
Patent Citation 2: JP-T-2007-511102